diff --git a/src/dui/outputs_n_viewers/img_viewer.py b/src/dui/outputs_n_viewers/img_viewer.py
index 853c4975..b9be3e57 100644
--- a/src/dui/outputs_n_viewers/img_viewer.py
+++ b/src/dui/outputs_n_viewers/img_viewer.py
@@ -288,6 +288,7 @@ def mousePressEvent(self, event):
 
     def mouseReleaseEvent(self, event):
 
+        mask_item = None
         if self.my_parent.chk_box_mask.isChecked():
             mask_item = build_mask_item(self)